As the capacity and performance of hard disks continue to advance, the ability to provide higher resolution track position signals for read/write heads of a hard disk assembly (HDA) is becoming increasingly important. In order to maintain the position of the magnetic head along the center line of a desired track, servo information in the form of a magnetic servo pattern is prerecorded on the disk surfaces during the manufacture of disk drives. The device used to record the magnetic pattern is called a servowriter and of course the accuracy of the servowriter will be critical to the accuracy of the resulting servo-pattern and the accuracy of the position of the read/write heads.
Recently the data density of hard disk drives has grown by 60% per year, and for example a storage density of up to 2.7 GB per square inch with a track density of up to 13,700 TPI (tracks per inch) is commercially available from International Business Machines Corporation. It is likely that in the near future even greater densities will be available, e.g. up to 50,000 TPI. Since when servo-writing a head position accuracy within 1% of the track pitch is required, these ever greater track densities place major demands on the servo-writer accuracy.